Various types of dispensers are used in many industries for placing liquids, such as adhesives, conformal coating materials, solder paste, solder flux, and other such materials, onto substrates during an assembly process. One such type of liquid dispenser is a syringe-type of dispenser having a dispenser body defining a barrel reservoir for holding a supply of liquid material to be dispensed. A dispensing tip may be coupled to the syringe at one end thereof and in fluid communication with the reservoir. A piston is disposed in the reservoir and is movable therein to pressurize the liquid in the reservoir so as to dispense a small amount of liquid from the dispensing tip and onto a substrate or the like.
Industrial applications may require that the liquid be dispensed in very precise volumes and at precise locations. To this end, liquid dispensers may include one or more actuators for moving the piston within the reservoir in a controllable and predictable manner. For instance, pneumatic actuators are known that use compressed air applied to the piston to move the piston and dispense liquid from the dispenser. Those of ordinary skill in the art will recognize that other type of actuators, such as linear actuators, may be used to control movement of the piston within the reservoir. In applications where such precise dispensing is not required, the piston may be moved through a manual process.
While such dispensing systems are widely used throughout industry and are successful for their intended purposes, users and manufacturers of these dispensing systems continually strive to improve their design and operation. For instance, in some applications current dispensing systems have some drawbacks. By way of example, in some instances dispensing one-part epoxies in such dispensers encounter premature curing of the epoxy while in the dispenser, which in turn locks up the dispenser and prevents its proper operation. The one-part epoxies may include microspheres of a catalyzing agent or hardener such that when the microspheres are burst or ruptured, the epoxy begins to cure. In normal operation, the epoxy may be dispensed onto a substrate and the microspheres subsequently ruptured through mixing or other mechanical action to cause curing of the epoxy. For instance, pre-applied thread lockers use one-part epoxies where the engagement between the threaded members causes rupture of the microspheres and curing of the epoxy.
Dispensers may utilize a piston that is formed from a relatively hard or rigid material, such as polyethylene. The rigid material of the piston reduces deformation of the piston when pressure or forces are applied thereto and may thus permit relatively accurate and precise liquid dispensing. When used for one-part epoxies, however, contact between the relatively hard piston and the microspheres may be sufficient to rupture the microspheres and cause curing of the epoxy in the dispenser. In this case, the dispenser may have to be discarded, which increases waste and thus increases costs.
The formation of the piston from a relatively hard material also has other drawbacks, such as sealing between the piston and the wall of the reservoir. In some applications, when manufacturing facilities are shut down or otherwise not in operation, activated or pre-mixed adhesives will often be frozen or cooled to extend their pot life and reduce the amount of adhesive discarded. Thus, the dispenser may be placed in a freezer or refrigerator to cool the adhesive and slow reaction rates. Once manufacturing recommences, the adhesives will be thawed and put back into operation. Such cooling/freezing of the dispenser may permit air to leak past the piston and into the reservoir. When the dispenser is thawed and put back in operation, the air may become entrained in the liquid causing burping or sputtering as the liquid is dispensed. Products may consequently have to be discarded, which increases waste product and increases costs.
In addition to issues discussed above, pressures developed in the reservoir during dispensing may, in some cases, be sufficient to overcome the seal between the relatively hard piston and the wall of the reservoir such that liquid may leak past the piston. Accordingly, there is a need for an improved dispenser and a method for making the same that addresses these and/or other issues of known dispensers.